I had a black 1979/80 Spitfire that I bought new in March of 80, the TT decals were lifting from almost day one, I complained, and the dealer re-decaled the bike the following fall. The guy at the dealer basically just rubbed the old decals off with a plastic razor bladeThe replacement decals, which I suppose were OEM Schwinn, lasted another 10 years before they yellowed and all but fell off in pieces.
A buddy owned a local sign shop at the time and he made me some vinyl stencils in the same font, I then sprayed the TT logos with automotive paint. The lettering was still in good shape when I sold it in the early 2000's. Looking back, I wish I had kept it though.